Method for the controlled addition of volatile treating materials

ABSTRACT

A process for adding volatile treating materials to molten metals with control of the final concentration of the material in the metal to remove impurities therefrom, and to impart advantageous properties to the metal.

United States Patent 5 1111 3,619,173

[72] Inventors Norman A. D. Parlee [56] Relerences Cited L Al Hi UNITED STATES PATENTS 2.678.266 5/1954 Zifferer 75/130 P 2.754.201 7/1956 2wicker 75/130 2.781.260 2/1957 Grandpierre 75/130 2.869.857 1/1959 Kopke et 3].... 75/130 x [73] lndusrks' 2.997.386 8/1961 Feichtinger 75/93 3.295.960 1/1967 Parlee et 111. .1 75/93 3.367.646 2/1968 Robertson et a1 75/130 X 54 METHOD FOR THE CONTROLLED ADDITION OF L Rm'edge Ass/111a"! E.IG"|| Ilt'f-G. Whlte 7 Claims, Drawing Auorney.rJames E. Toomey. Paul E. Calrow. Andrew E.

Barlay and Harold L. Jenkins [52] US. Cl 75/59, 75/93. 75/13() [5|] Int. Cl C2lc 7/00, ABSTRACT: A process for adding volatile treating materials C22b 9/00 to molten metals with control of the final concentration ofthe [50] Field of Search 75/129. material in the metal to remove impurities therefrom. and to 130, 93, 59. 49, 61 impart advantageous properties to the metal.

PAIENTEDunv 9 I9" $619173 T ARGO/V Mg F550 NORMAN ,4. D. PAELEE W/LL/AM E. MAN/N INVENTORS BYMTB-wkl ATTORNEY METHOD FOR THE CONTROLLED ADDITION OF VOLATILE TREATING MATERIALS BACKGROUND OF THE INVENTION There are certain materials which are volatile at elevated temperatures and which are very useful additives and treating materials for molten metals particularly ferrous metals. Examples of these materials are magnesium and calcium. Their use in the past has been quite limited because of their relatively low solubility in molten metals such as iron and their'great reactivity in the presence of air or oxygen over the molten metal being treated.

One of the principal prior uses of magnesium as a molten metal treating agent has been in the manufacture of so-called ductile iron. Ductile iron is a ferrous material which solidifies with free carbon in a spheroidal or nodular graphite form. The presence of free graphite in spheroidal form forms a material which has foundry and machining characteristics similar to gray iron with physical characteristics similar to steel. Magnesium is used as a desulfurizer and a residuum of magnesium is maintained in the metal at a low but significant concentration to bring about this great improvement in physical properties. In other words, the residual magnesium helps bring about the fon'nation of spheroidal graphite.

In the manufacture of pig iron, sometimes known as blast furnace hot metal, there is always some sulfur picked up from the ore and coke which leads to sulfur in the steel which is made from such metal.

Blast furnace metal could be made with little or no sulfur content; this would greatly benefit the economics of the steelmaking process and improve the quality of the steel produced. Accordingly, although the description of the instant invention will relate particularly to the manufacture of ductile or nodular iron, it should be appreciated that the instant invention for controlled additions of volatile treating material such as magnesium and calcium also applies to the treatment of liquid blast furnace metal, liquid malleable iron, gray cast iron or liquid steel as well as to other metals.

The methods used in the past for adding volatile treating material such as magnesium to iron have not provided very good control of the final magnesium content, which is quite critical and depends upon the original sulfur content of the iron. At one atmosphere total pressure magnesium boils at a temperature very much below the melting point of iron and at its boiling temperature often ignites explosively in air. Because of this, prior methods usually create a violent reaction and are hence somewhat dangerous. The atmosphere is polluted with the reaction products of the violent reactions and efficiency is low. For example, usually only about 30-40 percent of the magnesium added is found in the final iron analysis.

Various methods have been proposed in the prior art for making the magnesium addition to molten iron. While some of the prior art methods eliminate some of these difficulties, none of them eliminate all of the difficulties mentioned above. Another difficulty with some of the prior art methods for adding magnesium to molten metal is that since the magnesium is so readily oxidized and exerts considerable vapor pressure over the molten metal, e.g. iron, the iron rather quickly loses magnesium and hence the final product will not have the desired physical properties. Because of this it has been found necessary to add the magnesium to the iron immediately prior to its use in the foundry, a somewhat costly and cumbersome process.

With respect to ductile iron, it has generally been found in the past that best results are obtained when about 0.037 to 0.042 percent magnesium remains in the metal after treatment. Less than this amount of magnesium will not give adequate nodularization and more than the required amount causes centerline carbides and increased hardness plus dirty" iron. These magnesium concentrations are for irons containing about 0.015 to 0.02 percent sulfur. It is known that the general requirement for good ductile iron is to have magnesium contents of about 0.01 percent minimum in excess of the initial sulfur content.

Because of the difficulty with the prior art methods listed above, the production of ductile iron has generally required additions of magnesium of much more than 0.037 to 0.042 percent magnesium on a weight basis. A general rule of thumb for iron having a sulfur range of about 0.015 to 0.02 percent is that about 0.11 to 0.14 percent magnesium would be added but of this amount only about 35 percent is recovered in the metal, the rest going into the air as magnesium oxide smoke or into the slag or the refractory side walls of the vessel or lost in divers other ways.

The instant invention results in better separation of magnesium sulfides and will result in effective nodularization at low residual levels of magnesium, e.g. about 0.010 to 0.015 percent magnesium. The instant invention is applicable for removing sulfur and/or oxygen from various liquid metals such as titanium, zirconium, and ferrous metals, and particularly those ferrous metals containing carbon and silicon which are commonly known as cast iron, pig iron, malleable iron or ductile iron.

Thus, in general, the process is applicable to removing oxygen and/or sulfur from a broad range of metals especially those (liketitanium and zirconium) in which oxides and sulfides are especially stable.

The instant process provides a means of precise control of residual magnesium content in any molten metal and also provides means of efficient desulfurization and deoxidation of the molten metal with the volatile treating material such as magnesium or calcium. The process eliminates atmosphere pollution and provides essentially percent utilization of the volatile treating material. It has the further advantage of permitting treatment of large batches of metal which can be held in liquid metal inventory without loss of volatile treating agent until ready for use.

The method automatically controls the content of volatile treating material in the metal by controlling the vapor pressure of the volatile treating material. The volatile treating material is added to the system quickly and in some excess for optimum reactivity without any hazards arising from excess pressure. In the final stage of the process any excess volatile treating material is removed from the molten metal and stored in the system for reuse later.

According to the instant invention, a pool of molten metal is maintained in a vessel having a liquid holding portion and a vapor space. An innocuous atmosphere is maintained in the vapor space. An innocuous atmosphere is defined herein as an atmosphere that will not react in any undesirable way with or otherwise adversely affect the molten metal or the volatile treating material but which will perform the function of creating pressure and excluding undesirable gases. Examples of innocuous atmospheres are atmospheres that are substantially noble gases or, for some purposes, carbon monoxide and hydrogen. A preferred innocuous atmosphere is one that is substantially argon although others, for example helium, can also be utilized. As used herein, the term environmental control refers to a family of processes for improved metal making in a controlled innocuous atmosphere environment.

A liquid pool of volatile treating material is provided in a chamber connected via its vapor space to the vapor space of the vessel. One way to accomplish the connection is by at least two tubes running from one vapor space tothe other. One of the tubes is advantageously insulated and one of the tubes can be desirably cooled to a temperature below the condensation point of the treating material at the pressure of the system. The liquid pool of volatile treating material in the chamber is heated to vaporize a controlled amount of the material and to create a controlled partial pressure of the material in the system. The treating material vapors are cooled as they pass from the chamber to the vessel, for example by the cooling effect of the cooled tube, so that they condense and pass into contact with the metal being treated where some vaporization again takes place and a high concentration and high partial pressure of treating material vapor is formed over the metal being treated. lnnocuous gas is vented from the system as needed to maintain the desired total pressure and partial pressure of treating material in the system. It is possible that the resultant atmosphere would be substantially all treating material vapor. When the desired treating reactions are complete the temperature of the liquid pool of volatile treating material is reduced so that treating material vapors will condense back into the pool thereby lowering the partial pressure of the material in the system pulling volatile treating material out of the metal until equilibrium is reached with the desired concentration of treating material in the molten metal. innocuous gas is added as needed to establish the desired final total pressure and partial pressure of treating material to bring about this equilibrium. The reaction products are separated from the molten metal as needed so that the reaction may proceed in the desired manner.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic front elevation view of a device for practicing the instant invention.

DETAILED DESCRIPTION In the examples that follow, the drawing will be described with respect to a process for desulfurizing iron employing magnesium as a volatile treating material with a residuum of magnesium desired for the production of ductile iron although the invention, as has been stated and as will be seen, is broadly applicable to metals other than iron and processes other than desulfurizing and nodular or ductile iron making; In the examples it will be assumed that a magnesium concentration of about 0.015 percent is to be obtained and maintained in solution in the liquid iron at a temperature of about l,500 C. or 2,732 F. for the iron. The actual starting sulfur content can be ignored since the invention will be shown to automatically provide a variable amount of magnesium as needed to react stoichiometrically with all of the sulfur present and still obtain a predetermined final magnesium concentration. In all cases the final sulfur concentration is on the order of about 0.001 percent or less.

With reference now to the drawing, it will be seen that an elongated generally cylindrical chamber 10, herein referred to as a magnesium vaporizer, is positioned over a vessel 12 containing a pool of molten iron 14. The temperature of the mo]- ten iron 14 is measured and controlled automatically by a suitable device such as a two-color radiation pyrometer, not shown, the signal from which activates induction heaters 16 which heat the molten iron 14. The vessel 12 is maintained sealed and is initially filled with an innocuous atmosphere such as argon gas at least at one atmosphere pressure. In the chamber molten magnesium 18 is maintained at a suitable temperature by heating means not shown so as to create magnesium vapor in vapor space 20 at a partial pressure dependent upon the temperature of the molten magnesium 18.

The vaporizer chamber 10 is interconnected with the treatment vessel 12 by one or more relatively large tubes 22 which are capable of being maintained at elevated temperatures, for example by being insulated so that hot vapors from the treatment vessel 12 will rise through each such tube without significant cooling. At the same time, elsewhere and originating above the level of the of the liquid magnesium 18 in the vaporizer chamber 10 there are cooled tubes or condenser tubes 24 which may act as condensing surfaces to cause at least part of the magnesium to condense and fall as droplets of liquid into the treatment vessel 12 where it contacts the molten iron 14 and forms a vapor blanket thereover in the vapor space 26 of vessel 12.

As tubes 22 are relatively hot, while condensers 24 are relatively cool, there is a tendency for the hot vapors from the treatment vessel 12 to rise from the vessel into the upper portion or va or space 20 of the vaporizer l0 whence they tend to move downward again into the treatment vessel 12. Circulation of the vapors may also be encouraged by the pressure drop effect created by the condensation of magnesium in cooled tubes 24. Connected at the top of vapor space 20 are one or more tubes 28 which are cooled to a desired temperature, usually about 670 C. or l,238 F., i.e. to a temperature just above about the melting point so that nearly all magnesium vapor tends to be refluxed back into the pool of liquid magnesium 18. At the top of tubes 28 is a pressure relief valve 30 which is automatically controlled to maintain the desired pressure by a suitable control device indicated schematically at 32 as a resistant spring which will be opposed by the pressures generated in the system and when the pressures are greater then the spring pressure relief valve 30 will open. However, since only gases are normally present in the system in significant quantities, that is, argon and magnesium, and since most of the magnesium will be condensed back to liquid by the cooled surfaces of tubes 28, essentially all gas escaping through the pressure relief valve 30 will be argon.

Table I shows the approximate relationship at l,500 C. between the partial pressure of magnesium in the vapor phase and the weight percentage of magnesium in the molten iron.

It may be noted from table I that the system described above provides means for a two-step process. In the first step or stage of the process rapid entry of magnesium into the iron and therefore rapid reaction with any dissolved sulfur or dissolved oxygen present can be provided by heating the magnesium generator 10 so as to boil magnesium at whatever temperature has been preestablished for the system. In this step the system tends to pump magnesium vapor in concentrated form to the liquid iron 14 while removing any excess argon or other gases through the tubes 28 and out the pressure relief valve 30. The system quickly becomes essentially percent filled with magnesium vapor and therefore the partial pressure of magnesium in the vapor space 26 is substantially the same as the total pressure.

In the second step the temperature controls for the molten magnesium pool I8 and the cooled tubes 24 are set so as to remove the undesired excess magnesium from the liquid iron Mand return it back to the liquid magnesium 18 in the magnesium vaporizer chamber 10 while allowing argon to reenter the system to maintain the pressure at a preset level. This is done by lowering the temperature of the molten magnesium pool 18 and raising the temperature of the cooled tubes 24 to about the same point as the molten magnesium or perhaps very slightly higher than the temperature of the molten magnesium 18 to provide further driving force for the transfer of vapor. In this second stage or step the system tends to equilibrate with precise control of magnesium concentration in the treated iron and yet with no loss or waste of magnesium. In the second step or phase, valve 34 may be automatically controlled, for example by suitable pressure measuring means not shown, to allow argon or other passive gas into the system through pipe 36' as necessary to maintain the pressure preestablished at pressure relief valve 30 by the back pressure of control device 32 to compensate for the drop in the partial to fall through tubes 28 and 24 and mix with the magnesium vapor in vapor spaces and 26 until the mixture is essentially homogeneous and the partial pressure of the magnesium is in equilibrium with the molten iron pool 14 and the molten magnesium pool 18. Thus, the temperature of the molten magnesium 18 controls the concentration of magnesium in the liquid iron 14 at a given total pressure.

The instant invention will now be further illustrated by a specific example some of the data for which are presented in table ll which is derived from the approximate equilibrium relationship shown in table lll. Tables I, II, III and IV are intended to be illustrative of principles. The data are calculated from thermodynamic relationships.

speeded up by greatly increasing the driving force of magnesiurn dissolved in the liquid iron.

Initially, the treatment vessel is filled with fresh untreated liquid iron and the temperature adjusted to the desired control temperature l,500 C. or 2,732 F. As the metal enters, the pressure in the system is adjusted upwardly from about 1 to L2 atmospheres. Some of the argon is allowed to escape through pressure relief opening and this also provides periodic purging of the system. At the same time the automatic pressure control device 32 is adjusted to maintain 1.2 atmospheres of pressure in the system. The reflux tubes 24 are automatically controlled at about 670 C. or l,238 F. and the walls of the treatment vessel 12 are maintained above about TABLE 11 Operating conditions for manufacture of ductile iron Temperature C Pressure (atn10s.) Chemical analysis g, 8, per- Ptotal PM; at 26 percent pcoutml Operating stage C.) 12 18 24 28 setting Cent Begin treatment 1, 500 1, 137 1,137 670 670 1. 2 1. 0+ 0 0 0. 02 Treatment approx. half complete. 1, 500 1,137 1, 137 670-947 670 1. 2 l. 2 1. 2 2 0.085 0. 02 Overshoot- 1, 500 1,137 8 947 947 670 1. 2 1. 2+ 1. 2 0.085 0. 001 1, 500 1,137 947 947 070 1. 2 1. 2 0. 2 o. 015 0. 001 1,500 1,137 670 670 670 1.0+ 1.0+ 0 1 0. 015 0.001

1 Preferably the temperature should be about 1,137 C. or above. 2 Up to figure given. I 3 Outta figure given. U v

TABLE Ill M 947 C. or 1,737 F. and preferably about l,l37 C. or 2,079

30 F. or above so that there can be no refluxing of liquid magnesium by these walls. At this point the magnesium vaporizer 10 is 0 Magnesium Additions to Ductile Iron at 1 500C act1va ted by ma1nta1n1ng a temperature of about l,l 37 C. or 2,079 F. 1n the molten magnes1um l8 wh1ch 15 the bo1l1ng (Assume f for iron=5) point of pure magnesium for a pressure of 1.2 atmospheres. However, this temperature setting may be adjusted slightly up- Mg L1qu|d 1n... s P wards or downwards depending on the pressure in the system.

I IOn 0 [on If, for example, 1t is found that pressure before the vaporlzer T ac A was activated was 1.01 atmospheres and after the vaporizer Mam) was activate at l,l37 C. the pressure was only 1.18 at- 40 mospheres, then the temperature setting for the molten magggg 882 8-883 8%; nesium 18 would be moved upwards slightly until a pressure of 900 about 1.2 atmospheres was maintained. Conversely, if it is 947 0,21 0015 0.0005 found that the pressure relief valve 30 1s continually openmg 2 018 M2 and thus indicates that the system is working too hard to boil 049 g"; 8'33 'gf i magnesium, then the temperature could be adjusted slightly 1077 0.70 0.05 do downwardly 1 107 1.0 0.07 do Concentrated magnesium vapors now pass over w1th the cir- 3-35 do culating argon stream and condense in cooled tubes 24 and :2 drop onto the surface of the pool of liquid iron 14. Contact 1167 10 01 do with the hot iron immediately causes these droplets to par- 1347 5.0 0.36 do tially dissolve and boil and to form a vapor blanket just above :28 8-; 3 the iron surface. While maintaining operation of the control in this illustration the desired magnesium end point concentration in the liquid iron at l,500 C. will be only 0.015 percent. However, the amount of magnesium actually consumed will, of course, depend upon the sulfur concentration of the untreated iron as well as the small amount of oxygen which may be present in the iron.

Referring to table Ill, it will be noted that final equilibration will call for a partial pressure of magnesium of about 0.2 atmospheres to provide 0.015 percent magnesium in the iron and that this condition will be ultimately achieved by a temperature of magnesium in the vaporizer of about 947 C. or 1,727 F. This will be obtained with a partial pressure of one atmosphere of argon plus a partial pressure of 0.2 atmospheres of magnesium or a total essure of 1.2 atmospheres. However, the table also shows that if the process is fully utilized so that the total pressure of 1.2 atmospheres is maintained next to the liquid iron with the concentrated magnesium vapor being essentially the entire content of the gas, this will tend to be in equilibrium with 0.085 percent magnesium in the liquid iron. This shows clearly how the solution of magnesium can be speeded up and the desulfurization also systems described above, the temperature of the cooled tubes 24 is controlled to effect rapid transfer of magnesium from the vaporizer chamber 10 into the vapor space 26over the iron. By operating cooled tubes 24 at the lowest practicable temperatures, e.g. 670 C. which is only about 19 C. above the melting point of magnesium, there will be a rapid filling of the entire vapor space 26 over the liquid iron 14 with the concentrated magnesium vapor. However, once this space is filled and if the temperature of cooled tubes 24 is not adjusted upwardly, there will be a tendency for the vaporizer to overwork by refluxing the magnesium in the condenser tubes 28.

By having a sensitive temperature measurement of the condenser tubes 28, the point when this overworking commences can be detected and this point the temperature of the cooled tubes 24 is adjusted upwardly until the temperature measurement at condenser tubes 28 indicates that overworking has been eliminated.

Experience with operation of the system quickly teaches the approximate length of time required to achieve the desired degree of desulfurization of the iron in the first phase of the treatment. When this point has been reached the temperatures of the molten magnesium pool 18 and the cooled tubes 24 are brought to the desired equilibrium control temperature of 947 C. with the temperature of the cooled tubes possibly being a little bit higher than that, for example 950 C This results in a reversing of the cycle so that now the vapor blanket begins to disappear while at the same time the excess magnesium vapors condense as liquid back into the vaporizer vessel 10. Fresh argon enters through pipe 36 and valve 34 and mixes with the magnesium vapor to fonn a homogeneous gas consisting of 0.2 atmospheres magnesium and 1.0 atmospheres argon. Circulation and mixing of the gases take place naturally through thermal convection upwardly through tube 22 and downwardly through cooled tubes 24 because the gas over the liquid iron 14 is always being heated and tends to rise upwardly into the vaporizer chamber 10 where it is cooled to the controlled temperature before being returned to the reaction vessel 12. As the concentrated vapor blanket becomes dissipated, excess magnesium in the pool of molten metal 14 enters the gas phase and this also becomes deposited as liquid magnesium back into the magnesium vaporizer vessel 10.

With regard to the application of the method to the treatment of hot blast furnace metal or pig iron, it is evident from Table III that the most effective desulfurization requires a residual content of magnesium of at least about 0.01 percent. However, unlike the situation in the manufacture of ductile iron, this residual magnesium concentration is not necessarily desired in the steel made from the iron. This is no problem since it is to be expected that essentially all the magnesium will be oxidized and eliminated during the steelmaking process.

With regard to the application of the method to the removal of sulfur directly from molten steel, the main differences from the illustrations above are that the steel temperatures will generally be higher than for ductile iron or blast furnace hot metal and the f, (for steel), i.e. the activity coefficient of sulfur in the metal is approximately 1 for steel, as compared to 5 for ductile or cast iron so that a higher percentage of dissolved magnesium would be required to obtain the same percent of dissolved sulfur in the metal. Another difference is that low carbon steels contain a considerably higher percentage of dissolved oxygen prior to the treatment. The treatment of such steels with magnesium can result in both deoxidation and desulfurization to exceedingly low levels of dissolved oxygen and dissolved sulfur as indicated in table lV.

TABLE IV Desulfurization and Deoxidation of Low Carbon Steel at 1 600 C.

Assume f, for Steel 1 Data not available for Fe or Low Carbon Steel.

The reaction products, wither sulfides or oxides, may be separated from the bath in the treatment vessel from time to time by raking, scraping blowing or other means, as they are generally solid, floating on the liquid metal surface. All these techniques are used in one or another metallurgical treating systems today and hence are known to those skilled in the art. Whatever method is selected must be carried out in such a way that air would not be permitted to enter the vessel. Since the magnesium vapor is maintained over the molten metal at the desired equilibrium, there will be no tendency for redissolution of oxygen or sulfur as these solids accumulate. The mam reason for removing them is to avoid blanketing the surface of the metal to such a degree that the magnesium vapor and drops of liquid magnesium falling from the condenser tubes 24 do not make effective contact with the liquid iron or steel.

The use of an induction furnace which raises a meniscus in the metal and tends to push any surface material to the sides of the vessel is one way to maintain a solid-free area on the surface of the liquid metal. The material which collects on the sides can then be withdrawn as needed. Electromagnetic stirring devices can also be utilized where feasible to maintain a substantially open surface on the molten metal Mechanical stirring or mixing of the bath can also be used. Yet another method that can be employed to maintain a relatively open liquid metal surface is to employ a series of slanting jets of the innocuous gas, e.g. argon, which will tend to push the floating material to the side of the vessel. These can be relatively small jets of high velocity gas utilized from time to time as needed. The accumulated material can be withdrawn from sides of the vessel by suction through a sort ofvacuum cleaner" arrangement. Any gas which is sucked out along with the solids would then be returned to the treatment vessel. The materials of construction utilized for the system will depend upon the material being treated and the treating and alloying material being utilized. In general, however, they must be selected so as to be essentially nonreactive with the materials in the system they come in contact with at the operating temperatures and pressures of the system. With regard to heating and cooling of the surfaces of tubes 22, 24, and 28, and of the chamber 10, this can be done by wrapping" these with a proper combination of fluid cooled coils and electric resistance heaters. It may be noted that chamber 10 will also tend to receive heat from the condensation of vapors rising through tubes 22 and will tend to be cooled by the droplets of magnesium which fall through tubes 28. Likewise, tubes 22, 24, and 28 will tend to be heated by hot gases and at certain times by condensation of magnesium.

While there have been shown and described hereinabove possible embodiments of this invention, it is to be understood that the invention is not limited thereto and that various changes, alterations and modifications can be made thereto without departing from the spirit and scope thereof as defined in the appended claims wherein:

What is claimed is:

1. The process of adding a volatile treating and alloying material to a molten metal which comprises:

a. providing a closed furnace system comprised of a vessel having a molten metal holding portion and a vapor space and a vaporizer chamber having a portion for holding liquid treating material and a vapor space, said vessel and said chamber in sealed communication via their respective vapor spaces by at least two tubes, at least on of which is capable of being maintained at a temperature above the boiling point of the treating material and at least one of which is capable of being cooled to a temperature below the condensation point of the treating material;

b. maintaining a pool of molten metal in said vessel and a liquid pool of volatile treating material in said chamber while the system is under an innocuous atmosphere;

. heating the liquid pool of volatile treating material in the chamber to vaporize the material and create a controlled partial pressure of the material in said system;

d. passing the volatile treating vapors from the chamber into the vessel through said tube which is cooled so that the vapors condense and the resultant liquid droplets pass into contact with the molten metal pool where some vaporization of the treating material again takes place and high concentration and partial pressure of treating material vapor forms over the metal being treated;

e. returning of treating material vapor from said vapor space of said vessel to said vaporizer chamber through said tube maintained at a temperature above the boiling point of the treating material; and

f. reducing the temperature of the liquid pool of volatile treating material when the desired treating reactions are 3. The process of claim 1 including the following additional step:

a. when the desired treating reactions are complete, adding innocuous gas as needed to establish the desired final total pressure and partial pressure of treating material.

4. The process of claim 1 including the following additional step:

a. separating reaction products from the molten metal.

5. The process of claim I wherein the volatile treating material is magnesium.

6. The process of claim 1 wherein the volatile treating material is calcium.

7. The process of claim 1 wherein the molten metal is ferrous metal.

* I l I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,619,173 Dat d November 9 1971 Inventor(s) Norman A. D. Parlee and William E. Mahin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, Table II (left hand column) "Fnal" should be Final-; Column 5, Table II "asterik" (or 1 as used in patent) should be by 1,137 (2nd. Columu] Column 5, Table III (Column 3),"0.07" should follow 0.05 Column 5, Table III (Column 3) "1. 10'' should be 0.10 Column 6, line 39, "activate" should be activated Column 6, line 66, "and this" should be and at this Column 7, Table IV, "0.021" (Column 3) should follow 0.07

(Colunm 4) Column Table IV, "beard 0.006" should be 0.006 (Column 4) 7 Column 7, Table IV (Column 5) "9. 2 x 10 should be 9.2 x 10 Column 7, Table IV (Column 5) "1.3 x 10 should be 1.3 x l0 Column 7, Table IV (Column 5) "4 x 10 should be 6 4 X 10 Column 7, Table IV (Column 5) "2.3 10 should be 6 2.3 x 10 Column 7, Table IV (Column 5) "1.8 10 should be 6 l. 8 x l0" ---7 Column 7, Table IV (Column 5) "5.0 x 10 should be 5.0 x 10- Column 7, line 70,"wither" should be either and Column 8, line 57, "on" should be one Signed and sealed this 6th day of June 1972.

(SEAL) Attest: J EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents M o-1050 1069) USCOMM-DC 60376-9 9 \1 S GOVERNMENT PRINYINQ OFHCE |9690-366-33|5 

2. The process of claim 1 including the following additional step: a. when the volatile treating material is being vaporized, venting innocuous gas from the system as needed to maintain the desired total pressure.
 3. The process of claim 1 including the following additional step: a. when the desired treating reactions are complete, adding innocuous gas as needed to establish the desired final total pressure and partial pressure of treating material.
 4. The process of claim 1 including the following additional step: a. separating reaction products from the molten metal.
 5. The process of claim 1 wherein the volatile treating material is magnesium.
 6. The process of claim 1 wherein the volatile treating material is calcium.
 7. The process of claim 1 wherein the molten metal is ferrous metal. 